U.S. Pat. No. 4,329,153 discloses such a detecting device in the form of a testing tube. This testing tube is provided for detecting and measuring copper aerosols in air. The glass tube is frangible at its tips and a breakable glass ampule and a reaction layer are disposed one behind the other in the through-flow direction of the testing tube. The glass ampule is provided as a reagent supply vessel and the reaction layer of silica gel is provided as a carrier and is impregnated with a color indicator for copper. The ampule is filled with nitric acid and a filter layer is disposed between the ampule and the reaction layer. The filter layer holds back copper aerosols from the test quantity of air when passing the test quantity through the testing tube via suction.
After the sample has been taken, the ampule is broken and care must be taken that the entire contents of the ampule are distributed uniformly over the filter layer containing the copper aerosol as well as over the reaction layer having the color indicator.
The break of the ampule releases the reagent liquid immediately after breaking the ampule because of the way the ampule is mounted in the testing tube with the reagent fluid pouring directly onto the filter layer and the reaction layer before the residual amount is removed from the ampule. For this reason, color reactions take place before a uniform solution of the copper aerosols in the nitric acid and a uniform wetting of the reaction layer take place. This causes color changes to occur at certain locations of the reaction layer wetted with the detecting reagent; however, at other locations which are not yet wetted, the color change occurs only later. The non-uniform color change of the reaction layer resulting therefrom makes a reliable reading or comparison of the degree of color change with a color standard difficult.
In order to bring the entire contents of the ampule together with the test quantity to be investigated and the color reagent for a quantitative conversion, the content of the ampule must be driven out and applied to the reaction surface in a non-reproducible manner, for example, by means of whirling movements of the testing tube held in the hand with the open ampule. In this way, the reliability of the measurement method is essentially dependent upon the expertise of the user to manipulate the detecting device in a suitable manner.